1. Field of the Invention
The invention relates to a wide-viewing angle LCD technology, and more particularly to a wide-viewing angle LCD device with an electrode array suspended in an LC cell gap between two substrates which provides a transverse electrical field to drive LC molecules.
2. Description of the Related Art
Conventional TFT-LCDs (thin film transistor liquid crystal displays) devices, which use LC molecules with characteristics of rotary polarization and dual refractive effects so that incident light achieves bright and shade results, has a drawback known as a viewing angle dependency, that is, the contrast ratio decreases as the viewing angle increases. Thus presenting a difficulty in applying the TFT-LCD device to large-size display products.
Recently, various wide-viewing angle technologies have been proposed, such as an optical compensation film, a multi-domain vertical alignment (MVA) mode, and an in-plane switching (IPS) mode. The MVA mode LCD device uses a negative LC material, vertical alignment films, symmetrical protrusions and boundary electrical field effect, in which a pixel electrode array and a common electrode array formed on two substrates respectively provide a vertical electrical field to drive the LC molecules, thus increasing contrast ratio and response speed and solves problems of gray scale inversion and color shift. The IPS mode LCD device uses a TN (twisted nematic) LC material and a wide-viewing angle diffuser, in which a pixel electrode array and a common electrode array formed on a TFT array substrate provide a horizontal electrical field to drive the LC molecules, thus solves color shift caused by different viewing angles and increases the viewing angle.
EP No.0884626A2 discloses an MVA mode LCD device. FIG. 1A is a sectional diagram illustrating a conventional MVA mode LCD device. FIG. 1B is a diagram illustrating the variation in alignment of LC molecules shown in FIG. 1A.
In FIG. 1A, an MVA mode LCD cell 10 comprises an upper glass substrate 12, a lower glass substrate 14, and an LC layer 16 with a negative anisotropy of dielectric constant filling in the space between the two glass substrates 12 and 14. Two electrodes 18I and 18II and two vertical alignment layers 20I and 20II are formed on the inner surface of the glass substrates 12 and 14. In general, the upper glass substrate 12 serves as a color filter substrate. The lower glass substrate 14 serves as a thin film transistor (TFT) substrate where a plurality of TFTs and active matrix drive circuits are formed. The electrode 18II on the lower glass substrate 14 serves as a pixel electrode.
Furthermore, the LCD cell 10 has alignment-control structures including a plurality of first stripe-shaped protrusions 22I formed on the inner surface of the upper glass substrate 12 and sandwiched between the electrode 18I and the vertical alignment layer 20I, and a plurality of second stripe-shaped protrusions 22II formed on the inner surface of the lower glass substrate 14 and sandwiched between the electrode 18II and the vertical alignment layer 20II. When no voltage is applied, all the LC molecules are s aligned perpendicular to the vertical alignment layers 20I and 20II, respectively. For example, the LC molecules 16A are aligned perpendicular to the glass substrates 12 and 14. The LC molecules 16B above the protrusions 22I and 22II are perpendicular to the vertical alignment layers 20I and 20II, so that the LC molecules 16B pretilt at an angle to the glass substrates 12 and 14.
In FIG. 1B, after a voltage is applied to the LCD cell 10, the LC molecules 16A and 16B rotate toward a direction corresponding to an electrical field 24 to tilt at an angle depending on the voltage value. The arrows show the rotating directions of the LC molecules 16A and 16B. Within a pixel area, two alignment domains are formed at both sides of the first protrusion 22I or the second protrusion 22II. The LC molecules 16A and 16B disposed adjacent to the protrusions 22I and 22II has a pretilt effect before applying voltage, however, which conflicts with the rotating effect generated by the electrical field adjacent the electrode fringe after applying voltage, causing decreased response speed, disclination and poor viewing.
U.S. Pat. No. 5,995,186 discloses an IPS mode LCD device. FIG. 2A is a sectional diagram illustrating a conventional IPS mode LCD device. FIG. 2B is a sectional diagram illustrating the variation in alignment of LC molecules shown in FIG. 2A.
An IPS mode LCD cell 30 comprises an upper glass substrate 32, a lower glass substrate 34 and an LC layer 36 interposed in a space between the two glass substrates 32 and 34 and sandwiched between an upper alignment layer 38I and a lower alignment layer 38II. The lower glass substrate 34, serving as a TFT array substrate, comprises a plurality of TFTs, scanning lines, data lines, common electrodes, pixel electrodes and an active matrix driving circuit. The two adjacent electrodes 40I and 40II serve as a data line and a common electrode, alternatively a common electrode and a pixel electrode. After a driving voltage is applied to the IPS mode LCD cell 30, an in-plane electrical field 42 is generated between two adjacent electrodes 40I and 40II and parallel to the long axis of the LC molecules 36A, 36B and 36C so that the LC molecules 36A, 36B and 36C are rotated on the plane.
Since the data lines, common electrodes, pixel electrodes are provided on the lower glass substrate 34, the intensity of the in-plane electrical field 42 weakens as the in-plane electrical field 42 is distanced from the lower glass substrate 34. Thus, the intensity of the in-plane electrical field 42 for driving the LC molecules 36A or 36B is less than that for driving the LC molecule 36C. The LC molecule 36C adjacent to the lower glass substrate 34 where a higher intensity of in-plane electrical field 42 is applied, however, is difficult to drive on because of boundary conditions. The center of the LC layer 36, such as the LC molecule 36B, is more easily driven on but lacks a strong intensity of electrical field.
The present invention is a wide-viewing angle LCD device with an electrode array suspended in an LC cell gap between two substrates which provides a transverse electrical field to drive LC molecules.
Accordingly, the present invention provides a multi-domain vertical alignment (MVA) mode liquid crystal display (LCD) device. An upper glass substrate and a lower glass substrate are disposed parallel to each other, and a liquid crystal layer of positive dielectric anisotropy is formed in a space between the upper glass substrate and the lower glass substrate. A plurality of first protrusions is formed on the inner surface of the upper glass substrate. A plurality of common electrodes is formed on the tops of the first protrusions, respectively. A plurality of second protrusions is formed on the inner surface of the lower substrate, in which the first protrusions and the second protrusions are arranged alternately. A plurality of pixel electrodes is formed on the tops of the second protrusions, respectively, in which the pixel electrodes and the common electrodes are arranged alternately. After applying a voltage to the display device, a transverse electrical field is generated between the common electrode and the pixel electrode to drive the liquid crystal molecules, and two alignment domains are formed at both sides of the first protrusion.
Accordingly, the present invention also provides a multi-domain vertical alignment (MVA) mode liquid crystal display (LCD) device. An upper glass substrate and a lower glass substrate are disposed parallel to each other, and a liquid crystal layer of positive dielectric anisotropy is formed in a space between the upper glass substrate and the lower glass substrate. A plurality of first common electrodes is formed on the inner surface of the upper glass substrate. A plurality of second common electrodes is formed on the inner surface of the lower glass substrate, in which the second common electrodes are positioned corresponding to the first common electrodes. A plurality of protrusions is formed on the inner surface of the lower substrate, in which the protrusions and the second common electrodes are arranged alternately. A plurality of pixel electrodes is formed on the tops of the protrusions, respectively, in which the pixel electrodes and the second common electrodes are arranged alternately. After applying a voltage to the display device, a transverse electrical field is generated between the second common electrode and the pixel electrode to drive the liquid crystal molecules, and two alignment domains are formed at both sides of the protrusion.
Accordingly, the present invention also provides an in-plane switching (IPS) mode liquid crystal display (LCD) device. An upper glass substrate and a lower glass substrate are disposed parallel to each other, and a liquid crystal layer is formed in a space between the upper glass substrate and the lower glass substrate. A plurality of first protrusions is formed on the inner surface of the lower glass substrate. A plurality of second protrusions is formed on the inner surface of the lower substrate, in which the first protrusions and the second protrusions are arranged alternately. A plurality of first electrodes is formed on the tops of the first protrusions, respectively. A plurality of second electrodes is formed on the tops of the second protrusions, respectively, in which the first electrodes and the second electrodes are arranged alternately. After applying a voltage to the display device, a transverse electrical field is generated between the first electrode and the second electrode to drive the liquid crystal molecules.